OK. FTP into your account.
Move into the directory you want this installation performed under.
Create a new directory called 'cgi-bin'.
Go back to GT, and tell them that your CGI directory is:
No trailing slash.
Replace username with your username (your account name).
Replace domain with the domain you want this installed under, and the one you created your cgi-bin in.
The staff at GT are probably trying to find out the /home/username/domain part which they will not know with FTP.
Out of interest; who is helping you with this from GT?